Patent GB-406779-A (GB)
Title: Improvements relating to telephone systems
IPC: H04Q3/58
Filed: 1932-10-03
Abstract: 406,779. Automatic exchange systems. SIEMENS BROS. & CO., Ltd., Caxton House, Tothill Street, and CHRISTIAN, D. A., Morven, Charlton Road, Charlton, both in London. Oct. 3, 1932, No. 27409. [Class 40 (iv).] A discriminating selector-repeater at a satellite exchange comprises a hunting switch for extending calls to the main exchange, and a selecting switch for extending other calls and exercising the usual discrimination, the calling party being fed from the bridge in the selector-repeater in the case of some calls, e.g. local, or to an adjacent satellite or to the main exchange, whereas for other calls extended over the selecting switch, e.g. long distance calls, the feed bridge at the selector-repeater is replaced by a metallic circuit and the calling party is fed from a repeater connected to the outlet of the selecting switch. The repeaters connected to outlets of the selecting switch have ballast resistances and a higher voltage battery connected in the feed circuit as described in Specification 372,004 and 403,475. Local call. When the finder (not shown) associated with the selector-repeater, Figs. 1 and 2, is seized, ground on the negative wire operates A(i) followed by B, BA. The junction switch JA-JP hunts for an idle junction (absence of ground), and switching relay K operates, connects up dialling tone from lead DT, and completes the outgoing loop over D and I. When the line under has found the calling line A holds over the calling loop. The first digit is repeated by A over the junction and also to vertical magnet VM of the selector (wipers +, - P, M), C operating during the train and short-circuiting C(ii) to make it slow, while JG pulls up on the first impulse, locks and disconnects DT. The local call relay LD pulls up over vertical bank and wipers WX, WY when C falls back, locks up, operates ZM to release the selector and releases K to release the junction. JG falls back slowly and meanwhile maintains a ground wiper JP to busy the junction while the distant apparatus is releasing. When the selector reaches normal, A D pulls up and locks. The next digit is again repeated to VM, but JG does not now operate. CA however pulls up over (i) and at the end of the train when C falls back, RM interacts with G to hunt for an idle outlet on which H pulls up in series with G which remains inert. The circuit of CA(1) opened at the commencement of rotary stepping, but the relay held over CA(ii) in series with RM during stepping. Relay H switches through to the local second selector and connects ground over K(ii) in place of direct ground to the holding conductor of the finder. The winding K(ii) does not operate or hold the relay but is merely an impedance to prevent a short circuit of special trunk busy tone lead TBT when the selector is used for a long distance call as will appear later. The subsequent switches are set in known manner, the wanted party being rung from the final selector. When he replies, D pulls up and initiates operation of delayed metering relays DA, DB controlled by interrupters S, Z so that MP is operated and released to connect up a single pulse of booster battery. Call to adjacent satellite. The main differences between this and a local call in the circuit operations are that the selector does not drop back after the first digit and the metering relay MP is adapted to be connected over the fourth wiper M to interrupters P, Q for metering purposes. At the end of the first digit, the selected level is such that AD pulls up over the vertical bank and locks, followed by JD and LD which also lock. The seized main exchange junction is released as before, but as the circuit of ZM is opened and CA is operated, the selector now hunts for a junction to an adjacent satellite. The wanted line is selected and rung, and the operation of relay DB consequent to the reply of the wanted party, connects the metering relay MP to wiper M. The contacts of adjacent satellites in the bank of M are connected to leads M1-M3 according as to whether single, double or triple metering impulses are required, the double or triple impulses being supplied by interrupters P, Q during the period of operation of both relays DA, DB by interrupter Z. Call to main exchange. The selected level is such that JD operates but AD, LD remain inert so that the selector does not drop back, JG is not released, and the main exchange junction is held. CA pulls up, and the second digit is repeated over the junction and also to the rotary magnet of the selector for the purpose of selecting a metering lead over wiper M, CA falling back at the end of the train to prevent RM being further impulsed. The call is completed in known manner and metering takes place as described in the preceding paragraph. In the case of a single-digit call, e.g. to a manual position, the operation and release of DA consequent on operation of the answering relay D causes the rotary magnet RM to step the selector into the bank in order that the call may be metered. Release. In the connections so far described, release takes place on the relapse of A and B when the calling party hangs up. C pulls up during the slow period of B (relays I, D in the outgoing loop have relapsed) to delay the release of BA, the relapse of which releases the operated switching relay K or H, operates release magnet ZM, and releases AD, JD, LD, JG, if operated. The magnet ZM grounds incoming wire P to busy the selector during restoration. The junction switch homes and DB relapses. Busy release. In response to the busy signal, the calling party hangs up, but release is prevented from occurring during a flash period. If B relapses during such a period, I is energized by the battery on the + wire and closes a circuit for C which thus holds BA until the termination of the flash. An ineffective circuit for D is also completed in parallel with I. The engaged condition of the outlet is thus maintained until the flash terminates. Long distance calls. The selector is stepped to the tenth level, AD is operated, and the selector hunts for an idle outlet as in a call for an adjacent satellite. Relay NP is operated over post springs np when an outlet is found, cuts out the transmission bridge and extends the calling loop directly to a repeater, Fig. 3, at which L operates in series with ballast resistances BR. Trunk busy tone from TBT is also connected by NP to the private wire of the calling party to warn another operator on attempting to make connection with his line. Relay A is held over (i) and wiper M of the selector dependent on IR which energizes in the loop outgoing to the operator and also busies the selector independently of H. If the calling party hangs up after the operator answers, L falls back, but IR holds over the + wire, polarized relay R remaining inert. When the operator re-calls, the battery on the + wire is replaced by booster which holds IR and operates R to connect up ringing current. When the operator clears, IR falls back and releases A, L having been released by the calling parts, and release then ensues as described previously. All outlets busy. If all outgoing main exchange junctions are busy, K operates on last contacts which are not multiplied to those of other junction switches, and operates an overflow meter over OM. A call other than over the junctions proceeds as previously described, but in case of a junction call, JD operating at the end of the first digit connects busy tone to the - line. If the bi-directional switch proceeds to eleventh contacts, H pulls up, eleventh step springs S connect busy tone and prevent the operation of NP in case of a long distance call.